Fix unsupported routes in Rails 6

`nil` format is not supported and throws an exception

Regex anchors in constraints are also not supported anymore. These
shouldn't be needed anyway

config/routes/project.rb

@@ -58,7 +58,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
             get :trace, defaults: { format: 'json' }
             get :raw
             get :terminal
-            get '/terminal.ws/authorize', to: 'jobs#terminal_websocket_authorize', constraints: { format: nil }
+            get '/terminal.ws/authorize', to: 'jobs#terminal_websocket_authorize', format: false
           end
 
           resource :artifacts, only: [] do
@@ -228,7 +228,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
             get :metrics
             get :additional_metrics
             get :metrics_dashboard
-            get '/terminal.ws/authorize', to: 'environments#terminal_websocket_authorize', constraints: { format: nil }
+            get '/terminal.ws/authorize', to: 'environments#terminal_websocket_authorize', format: false
 
             get '/prometheus/api/v1/*proxy_path', to: 'environments/prometheus_api#proxy', as: :prometheus_api
           end
@@ -328,13 +328,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
           get :test_reports
           get :exposed_artifacts
 
-          scope constraints: { format: nil }, action: :show do
-            get :commits, defaults: { tab: 'commits' }
-            get :pipelines, defaults: { tab: 'pipelines' }
-            get :diffs, defaults: { tab: 'diffs' }
-          end
-
-          scope constraints: { format: 'json' }, as: :json do
+          scope constraints: ->(req) { req.format == :json }, as: :json do
             get :commits
             get :pipelines
             get :diffs, to: 'merge_requests/diffs#show'
@@ -344,6 +338,12 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
             get :cached_widget, to: 'merge_requests/content#cached_widget'
           end
 
+          scope action: :show do
+            get :commits, defaults: { tab: 'commits' }
+            get :pipelines, defaults: { tab: 'pipelines' }
+            get :diffs, defaults: { tab: 'diffs' }
+          end
+
           get :diff_for_path, controller: 'merge_requests/diffs'
 
           scope controller: 'merge_requests/conflicts' do
@@ -372,16 +372,16 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
         scope path: 'new', as: :new_merge_request do
           get '', action: :new
 
-          scope constraints: { format: nil }, action: :new do
-            get :diffs, defaults: { tab: 'diffs' }
-            get :pipelines, defaults: { tab: 'pipelines' }
-          end
-
-          scope constraints: { format: 'json' }, as: :json do
+          scope constraints: ->(req) { req.format == :json }, as: :json do
             get :diffs
             get :pipelines
           end
 
+          scope action: :new do
+            get :diffs, defaults: { tab: 'diffs' }
+            get :pipelines, defaults: { tab: 'pipelines' }
+          end
+
           get :diff_for_path
           get :branch_from
           get :branch_to

ee/config/routes/group.rb

@@ -152,7 +152,7 @@ end
 
 # Dependency proxy for containers
 # Because docker adds v2 prefix to URI this need to be outside of usual group routes
-scope constraints: { format: nil } do
+scope format: false do
   get 'v2', to: proc { [200, {}, ['']] }
 
   constraints image: Gitlab::PathRegex.container_image_regex do

ee/config/routes/project.rb

@@ -25,7 +25,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
 
         resources :jobs, only: [], constraints: { id: /\d+/ } do
           member do
-            get '/proxy.ws/authorize', to: 'jobs#proxy_websocket_authorize', constraints: { format: nil }
+            get '/proxy.ws/authorize', to: 'jobs#proxy_websocket_authorize', format: false
             get :proxy
           end
         end

ee/lib/ee/gitlab/path_regex.rb

@@ -11,7 +11,7 @@ module EE
         end
 
         def container_image_regex
-          @container_image_regex ||= %r{\A([\w\.-]+\/){0,1}([\w\.-]+)\z}.freeze
+          @container_image_regex ||= %r{([\w\.-]+\/){0,1}[\w\.-]+}.freeze
         end
       end
     end

ee/spec/lib/ee/gitlab/path_regex_spec.rb

@@ -10,7 +10,13 @@ describe Gitlab::PathRegex do
     it { is_expected.to match('gitlab_foss') }
     it { is_expected.to match('gitlab-org/gitlab-foss') }
     it { is_expected.to match('100px.com/100px.ruby') }
-    it { is_expected.not_to match('foo/bar/baz') }
-    it { is_expected.not_to match('ruby:2.3.6') }
+
+    it 'only matches at most one slash' do
+      expect(subject.match('foo/bar/baz')[0]).to eq('foo/bar')
+    end
+
+    it 'does not match other non-word characters' do
+      expect(subject.match('ruby:2.3.6')[0]).to eq('ruby')
+    end
   end
 end